1. Brief Description of the Prior Art
In running a string of drill pipe or casing into an oil and gas well, it is necessary to make up the string by threadedly interconnecting sections of the drill pipe and casing. This has been done in the past in two ways. In both methods a first section of drill pipe, which is to be connected to a second section which is held by slips in the rotary table on the drilling platform, is suspended from the mast of the derrick so that the lower end of the suspended section of pipe is immediately above, and in contact with the lower section of pipe into which it is to be threaded. In the safest, but most expensive method of threadedly engaging the pipe sections, the upper section of pipe is gripped by a power tong and is rotated about its axis by the use of such tong. The power tong is a large mechanical structure having gripping jaws which are open at one side and in the center, and which includes a geared-driven ring which forces dogs or grippers radially inwardly to clamp around the drill pipe. The gear ring-engaged dogs are then caused to undergo rotation about the axis of the pipe so that the suspended section of pipe is rotated and threaded up tightly into the section of drill pipe therebelow.
Examples of power tongs used in this way for coupling sections of drill pipe or casings are illustrated in U.s. Pat. Nos. 2,550,045, 2,573,212, 4,357,843, 1,923,010 and 1,955,727.
In U.S. Pat. No. 3,086,413, a power operated spinner mechanism is applied to a free standing section of pipe supported from the crown block swivel and is powered to spin up the pipe to a slightly tight connection to the section of pipe held in the slips on the drilling platform. A manual pipe tong is then used to tighten up the upper section by manual power to the final desired make up of the tubing string. The power operated spinner is said to be light enough to be transported from one job to another, and is universal in the sense of susceptibility to mounting upon any conventional manually operated tubing tong.
in general, power tongs of the type described include a power source which drives a gear train through which power is transmitted to a ring or ring segment which is rotated in a forward or reverse direction, depending upon whether the pipe or casing section is to be coupled (screwed up) or uncoupled (unscrewed). The ring or ring segment carries camming structures which function to cause dogs or engaging clamps or teeth to move radially inwardly against the upper pipe section which is to be coupled to a lower section. Continued movement of the ring or ring segment then causes the dogs or clamps to be rotated about the axis of the pipe, causing it to be screwed up tightly, or unscrewed, as the case may be.
Where power tongs are employed for threadedly engaging the pipe sections, there is much less risk to personnel than when manual means is utilized for making the engagement. Because of the expense of using power tongs, however, and the fact that on some types of drilling rigs, power of the correct type is not available for powering the tongs, manual means for threadedly engaging the pipe or casing sections continues to be widely employed. One of the most frequently used methods for coupling pipe sections is by use of a so-called spinning chain. In this method, one of the rig crew throws the free end of a spinning chain so as to make the chain wrap around the pipe section which is to be threaded into the next lower section. A line is then run from the spinning chain to a cat head winch. The winch is used for pulling the chain, and in pulling the chain, to cause the pipe section about which it is wrapped to undergo rotation and to become threaded into the next lower section. The use of a spinning chain to accomplish this threaded engagement is dangerous, and very frequently results in serious injuries to the chain thrower or to personnel standing near the place where the chain is used for this purpose.
Even in those instances where a spinning chain is used for effecting threaded engagement, this generally tightens the pipe joint or connection up to only a limited extent. Manual tongs are then used for applying the final torque to the pipe section to tighten it to a pre-determined extent in the joint.
In U.S. Pat. No. 4,306,471, the patentee endeavors to achieve the relative economy of manually spinning up a pipe section when making a threaded connection while substantially enhancing the safety with which this method can be employed over those spinning chain methods previously in use. The inventor provides a pipe spinner apparatus which includes a pair of jaws which clamp about the pipe, and which further includes a serrated inner surface on the jaws which can grip the pipe when the jaws are closed. An outer jaw subassembly is provided to engage a chain or other flexible tension member which can be extended into engagement with the outer jaw subassembly for driving the pipe engaging elements in rotation. The chain is extended to a cat head, and it is unnecessary for workmen to throw a spinning chain or hold it in tension at the time that it is being pulled by the cat head. Thus, while a typical and conventional cat head chain device can be utilized to apply the power that rotates the pipe, there is no requirement for wrapping the chain several times about the pipe, and the workmen is isolated from the point of power application and thus can perform the method with enhanced safety.
U.S. Pat. No. 4,346,631 discloses an improved power source useful for pulling a spinning chain to initially spin up the pipe section to a relatively loosely coupled status, followed by the use of the same power device for applying force to one end of an elongated arm forming a part of a tong used to accomplish final torquing of the pipe section to achieve a tight joint. The power device employed is a piston and cylinder arrangement in combination with certain sheave devices which operate to pull the chain, and also function, at the time when final torquing is to be accomplished, to rotate the tong by coupling a cable to the end of the tong lever arm, and extending it over a suitable pulley and sheave arrangement used in conjunction with the piston and cylinder.